AUC/MIC: a PK/PD index for antibiotics with a time dimension or simply a dimensionless scoring factor?

A previous article on standardization of pharmacokinetic/pharmacodynamic terminology for anti-infective drugs recommended deletion of the units of the AUC/MIC ratio (actually h). We express here the difficulties presented by this proposal and we propose expressing AUC/MIC as a scaling factor corresponding to the current index divided now by 24 h. This is the scaling factor without units by which the targeted MIC should be multiplied to estimate the average in vivo plasma concentration to be achieved. Associated with this proposal, we address the specific issue of veterinary drug products for which steady conditions are seldom achieved. To accommodate the need for dose prediction during these novel therapeutic situations, we propose a general approach that is based on the targeted time interval over which some desired average concentration should be maintained.